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RA: 10h 17m 50.55s
Dec: −62° 40′ 14.6″
Ch: MSA:992, U2:449, SA:25
Type: planetary nebula
Mag: B=19.4, V=?
This planetary nebula was discovered by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "planetary nebula, delicate, exactly round, = * 10 mag a little dim at edges; white; with 320 [power] considerably hazy. In field with at least 150 stars." His second observation records it as "perfectly round; very well defined, with a perfectly uniform light, not at all mottled; = a star 10th mag, of which brightness there are 5 or 6 more in the field, and not less than 150 others less bright. Examined by both Mr Maclear and myself with 240 [power] which shows it proportionally magnified; quite round and planetary; a little hazy at the edges, but not more so than is due to the decidedly bad definition of the night, and the imperfect figure of the mirror, which has been injured by careless polishing on too soft a polisher."
The NGC records it as "planetary nebula equal to star of 10th magnitude, round, amongst 150 stars."
A photographic survey of bright southern planetary nebulae. M.N.R.A.S., 110(5), 429-439.
"The object (Fig7) is a bright disk 14'' in diameter, with a slight bump on the northern edge. The central star is barely visible."
Burnham calls it faint, small and round. Modern catalogues give it a magnitude of 11.8 with a 12 arcsecond diameter.
(Sulentic and Tifft 1973) notes that this is a 12.0 mag planetary nebula.
From: "Neat Southern Planetaries - X."
The regions in Argo Navis are rich in planetary nebulae. In all, Pyxis contains four; Puppis thirteen; Carina twenty-two, while Vela contains the most, with thirty-three. However, of the seventy-two Argo planetaries, most are below c.5"sec.arc. About half of these are no only small but faint, and give decent challenges for amateurs to find, even for those with larger apertures. The problem that remains is identification because of the star-packed fields. Not having a UHC or O-III filter, makes finding them almost unsurmountable - unless we take due care.
Sometimes I think looking for faint deep-sky objects and 'pushing the photon envelope' is perhaps a bit like fox hunting. It takes a bit more cunning and ingenuity to 'out smart' the object, who hides among all the field stars, almost wishing to avoid capture! Overall, observers seem to have more appreciation for an object that took half-an-hour to find, than the one that is obvious at first glance. Personally, I have seen people get so frustrated - that they would never find their target just because of their attitude. My advice is not to worry if you do not find an object. You can have more fun finding a few 'surprise' objects on your way to your goal!
Selected is a planetary 'pair'; NGC 3211, IC 2553, followed by the challenging Sanduleuk pentad; SA2-61; SA2-64; SA2-65; SA2-66; and SA2-68. The last five all lie within a 2.2° field, which I have termed 'The Five Planetaries'. For the observer this region has a wealth of objects for amateur eyes, and I have selected the most interesting. Included for the surrounding objects are; two field variables, a challenging cluster or two, and some brilliant pairs. (Note: If you do not like the selected pairs this month - then I will know such observers will never become connoisseurs of double stars.)
NGC 3211 / He2-46/ SA-59/ WRAY 16-70/ HJ 1837/ PK 286-4.1(10178-6240) (Car.) is a bright planetary placed some 3.3° northeast of the Southern Pleiades, and 1.2° south of the 3.4 magnitude orange star q Velorum. Within the field, some 20'min.arc of the planetary is two 6.9 and 8.4 magnitude stars, some 6' apart. Discovered by John Herschel in 1837, the object is easily found in a 10cm. or 15cm. An O-III is a godsend, helping to isolate the planetary from the surrounding starry field. The NGC description is the same as given by John Herschel - 'F, S, B -faint, small, bright', and is type 2b - a smooth disk with uniform brightness. Visual magnitude is about 10.0 to 10.2 (brighter than some reference sources), while the photographic magnitude is 10.7.
A few amateur quotations are available, they include;
AOST2 (pg.189) states; "In a beautiful starry field is a small even pale blue disk... fairly bright with no visible central star and a single prism image.... An [OIII] filter helps with small apertures."
Andrew Murrell (Universe 42,3 1995) in his article entitled "Carina";
"NGC 3211 is a planetary nebula about 12" in diameter and a surface brightness of about magnitude 10.5. This nebula could be a challenge for a 4" scope. The surface of the nebulae is smooth. The central star is not visible in Hector (Andrew's 20".)"
J.Graham Little (Southern Sky 1,4 pg.54) says NGC 3211 is;
"A smallish, faintish planetary, 3211 has a diameter of 12 and a mag. of 11.8. It appears, very simply, as a fairly evenly illuminated disk with a grey-blue colouring. A 15cm. 'scope will find this a bit of a challenge."
Apparent visual diameter is some 12"sec.arc., that seems to increase with aperture. Like last month's IC2448, some debate exists on the true diameter. AOST1 states 10"sec.arc., while AOST2 gives it as 12" and Burnham's gives it as 14"sec.arc. Using the "Strasbourg - ESO Catalogue of Galactic Planetary Nebulae"; Acker et.al. (1992) the diameter is 16"sec.arc. It seems the reason is the gradual fading of brightness near the outer edges of the planetary. Therefore, the bigger the aperture, the larger the planetary. As a multiple shell planetary, this is an expected property. In the largest telescopes the diameter extends to 23"sec.arc. (1971), while the infrared image is 33"sec.arc, with a strong flux at 100Ám. (microns).
Radial velocities suggest NGC 3211 is moving towards the Sun at -22.0kms-1▒2.0 (1983), while the spectrum reveals a mean expansion velocity of 29kms-1. The entire nebulosity is 0.1 solar masses, with an electron density is 1 000 e-.cm-3.sual magnitude of the PNN (HD 89516) is 14.22, but some sources, like Sky Cat. 2000.0 and Megastar, incorrectly quote the older 'B' Mag. of 18.0. Although it is a 'B' spectral type - though this does not easily reconcile with the higher 130 000OK Zanstra temperature. Early estimates said the temperature was 66 200OK, though another estimate by the 'Stoy Method' or 'Energy Balance Method'; suggests 135 000OK., which is based on H measurements and the amount of ionization. In 1993, another independent result gave the same temperature. These huge variations are typical, as all 'B' stars are notorious for having a wide range of surface temperature. If the Zanstra temperature is true, then the relative luminosity must be 870 times brighter than Sol and the absolute visual magnitude is 4.67. NGC 3211, like last month object IC 2442, also shows weak indication of the P Cygni Phenomena. Once, we estimated that this PNN was c.0.4 Solar Masses. Later estimates are closer to 0.67 ▒0.09. This suggests the progenitor was once between 1.0 and 1.3 solar masses.
First, we gave NGC 3211's distance as 1.91kpc., but later studies today favour around 3.3kpc. AOST2 is the closest of all the amateur reference, giving the distance as 3.0kpc. Based on the extinction magnitudes, Pottasch derives a distance of 2.5kpc. The mean value, based on the statistical distances, (1971-1994) is about 2.7kpc. Based on the 3.3kpc. distance, the true size of the planetary is 0.42 ltys. or 40 billion kilometres across - eight times the diameter of the entire Solar System! Some estimates place the evolutionary age of the inner bright luminous shell as young as 4 500 years. On a human scale, this dates to the earliest literary writings - like the 'Epic of Gilgamish'.
In all, this is another good example of an easy bluish-grey southern planetary.
Hartung writes: "In a beautiful starry field is a small even pale blue disk about 10 arcseconds across, fairly bright with no visible central star and a single prism image. It may be picked up easily with a four-inch, but both nebula and prism image need care with a 3-inch."
QBS: 20" diam, but OX.
15cm - obvious circ patch @ 80x. 295x/410x: circ annulus 12" diam, sl dimmer on SE side. hole is 1/4 total diam. no cen *. m10-10.5, sl fntr than I2553 nrby when compared w/o filts @ 80x. strong UHC, vstrong [OIII] enhancements. BS, 18Feb1990, LCO.
Date: 2010 February 12/13 (second session).
Location: "Sterland", Sutherland.
Telescope: "Bertha" 12-inch f/4.8 Dobsonian.
Sky conditions: Dark sky, seeing very good, transparency high.
Star chart: MSA 1005
In the 32mm (45x) it appears as a bloated 11th mag star (being of similar brightness to two companion stars which make a triangle with it - one due south, the other WSW, about 5' distant).
At 115x (B+25mm) the planetary shows a small disc, sharply terminated, with an even light across its surface.
The Messier objects
The Bennett objects
The Caldwell list
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